1) Field of the Invention
The present invention relates to drive wheels used on vehicles and particularly to plastic wheels used for driving vehicles such as lawn and garden tractors and rear engine riders.
2) Related Art
Walk behind lawn mowers have long used plastic wheels due their low cost and light weight. In some applications, the plastic wheels serve as drive wheels. Some plastic drive wheels have been bolted to hubs that are driven by transmission axles.
Others have been mounted on axles and provided with gear teeth that are in turn powered by transmission driven axles provided with a pinion fixed to their end portion. The gear teeth can either be carried on the inside periphery of the wheel or on a gear mounted co-axially with the wheel to engage the axle pinion. Both plastic and metal gears have been used in combination with such plastic drive wheels.
Plastic wheels used on walk behind lawn mowers are typically much smaller than the wheels which would be required on larger vehicles such as lawn and garden tractors or rear engine riders. To simply enlarge plastic lawn mower wheels for use on the larger vehicles could present problems.
For example, to power large vehicle drive wheels through the use of teeth on the inside face of the wheel would allow only the outside face of the wheel to be used to support the weight of the vehicle. Since larger vehicles weigh more, support drivers and often carry or support attachments, the use of only the outside face of the wheel for support would not be desirable.
Further, plastic drive teeth incorporated into the inside face of a drive wheel used on larger vehicles, whether molded into the inside periphery or carried on a co-axially mounted plastic gear, could result in rapid or premature wear due to the higher torque requirements found with heavier vehicles.
One approach which has been used to inhibit wear and/or premature failure of drive teeth has used a metal gear mounted on the inside face of the plastic wheel. While metal gears can be expected to wear much better than plastic gears, their cost can be high. Further, they increase vehicle weight and present additional expense for assembling them to the drive wheel.
Another approach utilizes metal wheels and metal gear teeth. While these wheels and gears would provide sufficient strength and wear life for larger vehicles, their cost and weight are prohibitive.
An additional problem encountered when adapting plastic wheels for use with larger vehicles relates to the torque levels that must be transmitted from the transmission axle to the drive wheel. When a pinion is used on the axle to drive the teeth on the wheel, bending forces can be encountered at the end portion of the axle.
Therefore, to avoid rapid wear and/or premature failure of the wheel, it would be desirable to provide a plastic drive wheel usable with larger vehicles that does not require the use of bolts or similar attachment devices to couple it to a hub, nor the use of plastic teeth formed in or attached to it. Further it would be desirable to provide a plastic drive wheel that can support the heavier weight of larger vehicles. Additionally it would be desirable to provide a plastic drive wheel that is not prohibitively expensive to manufacture and/or assemble, is reliable in operation and is adapted to reduce the bending forces transferred to the drive axle with the higher levels of torque expected on heavier vehicles.